Basically in hydrology, underground storage of water is referred to as an AQUIFER.
An aquifer is a geologic formation that contains water and allow water to pass through them examples are sandstones,dolomites,limestone, quartz,unconsolidated rocks .e.t.c.
Aquifers are useful for recharges of wells and boreholes.
An aquifer can be grouped into two types which are the confined and unconfined aquifers.
Confined aquifer: this type of aquifer is also called the water table,when they are excavated: they operate freely under the influence of the atmospheric pressure. The lower boundary is impervious layer(clay) while the upper boundary is the water table.
Unconfined aquifers: the upper and lower boundaries are bounded with impervious layers(clays) such that the water are compacted with such a great pressure, the upper boundary is called the piezometric surface,they are also called the artesian wells.
An artesian aquifer is a confined aquifer containing groundwater under positive pressure. This causes the water level in a well to rise to a point where hydrostatic equilibrium has been reached.
A well drilled into such an aquifer is called an artesian well. If water reaches the ground surface under the natural pressure of the aquifer, the well is called a flowing artesian well.
The roles of aquifers cannot be overemphasized in water resources management and development. Human would have been depending on precipitation only e.g. rain, for daily consumption of water which is not readily available always which is also a merit of the aquifer.